if you haven't already, go to View and select "Show Coins" in Electrum, a new tab will show up called "Coins". there you can see all your unspent transaction outputs that you own. among these the low value transactions are dust.
the amount that is considered dust by the network has changed many times so now i am not sure how it is calculated today. last i checked it was 546 but that is for sending that amount not spending it if you have it.
for spending you pay a fee and depending on how much the fees are at any time, you can consider different levels for dust. right now with low fees anything below 0.0002BTC-0.00002BTC with normal fee and low fee respectively can be spent without losing much to the fees. read this for more info: https://bitcointalksearch.org/topic/aug-2022-mempool-empty-use-this-opportunity-to-consolidate-your-small-inputs-2848987